Incorporation of replaceable cylinder liners in the design of an internal combustion engine provides numerous advantages to the manufacture and user of such an engine. In addition to the obvious benefit of allowing such liners to be replaced during overhaul of the engine without replacement of the entire cylinder block, cylinder liners eliminate the necessity to scrap the entire block during manufacture should the inside surface of one cylinder being improperly machined. Despite this and other advantages, numerous problems attend the use of replaceable cylinder liners as is exemplified by the great variety of liner designs previously used by engine manufacturers. While each of the previously known liner designs exhibit their own distinct advantages, no single design appears to provide a liner design wherein an increase in bore diameter is achieved without the need to increase the distance between the cylinder centers, thus allowing increased sweep volume from an existing engine.
Additionally, there is a trend in the industry to increase the output of internal combustion engines by increasing the firing pressures and thermal load of the engines. This trend has tended to favor the adoption of wet type liners in a cylinder block where the liner is in direct contact with a cooling medium over an extended portion of its length thereby providing improved heat transfer and allowing the operation of engines at higher firing pressures and increased thermal loading.
However, conventional wet type cylinder liners have several disadvantages. Since the wet liner requires substantial space for the cooling liquid, the use of such liners substantially increases the distance between the a center lines of the several cylinders, this increase being necessary to ensure space for cylinder block and liner walls of adequate thickness to withstand the increased mechanical and thermal loads and to resist cavitation erosion. Also, this increase is necessary in order to provide room for a flange to support the wet type liner in the cylinder block. The greater distance between the cylinder bores, of course, increases the overall length of the engine, and thereby adds cost, weight and bulkiness to the engine.
Wet liners also require the installation of seals between the lower portion of the liner and the cylinder block to prevent the cooling medium from migrating into the oil and vis versa. These seals are susceptible to damage and adversely effect engine reliability and durability, and increase maintenance costs. On the other hand, a fully dry liner where the liner is separated from the cooling medium throughout its entire length also has several disadvantages. The heat transfer between the liner and the cooling medium is restricted because the coolant flow is disrupted by cast cylinder head screw bosses located around the upper portion of the liner. Also, it is difficult and expensive to cast clean cooling passages around the liner supporting the structure of the cylinder block. Finally, the dry type liner has a lesser capacity for heat dissipation from the liner than the fully wet liner and thus does not readily accommodate the trend toward increased firing pressures and thermal loading presently encountered in internal combustion engines.
Presently, both wet and dry type cylinder liners incorporate either a mid-stop arrangement wherein the cylinder liner is substantially supported within the block mid-way along the length of the cylinder liner or a top stop wherein the cylinder liner is supported about an upper periphery thereof. U.S. Pat. No. 3,403,661 discloses a liner design for use in an engine block having a counter bore cylinder cavity wherein the liner includes a radially outwardly extending flange designed to be seated in the counter bore so that the liner may be easily clamped into place by the engine cylinder head. In order to provide for coolant flow around the liner, a seal is provided between the engine block and a lower portion of the liner spaced from the top flange. Due to vibration and thermally induced size changes of the liner, relative motion occurs in the seal area of a type which may destroy conventionally known seals. This is particularly true since coolant passages are normally formed in a manner to cause particles within the coolant to collect in the seal area and eventually work between the seal surfaces resulting in hastened seal destruction.
One possibility for solving the coolant seal problem would be to move the block engaging flange of the liner to the lowermost point in the coolant passage such as is illustrated in U.S. Pat. No. 3,315,573 issued to Castelet. This approach, however, leads to head gasket seal problems due to the unequal thermal expansion of the block and the liner. While such top seal leaks may be solved in part by the provision of a composite liner having a thermal expansion coefficient more nearly equal to that of the engine block, the provision of such a composite structure measurably increases the manufacturing costs and is thus not an optimum design.
Some manufacturers have resorted to complicated compliant or even resilient seals to accommodate size changes due to thermal expansion such as that illustrated in U.S. Pat. Nos. 3,628,427 and 3,882,842. The liner designs illustrated in these patents present additional problems by the virtue of the provision of an upper liner portion which is out of direct radial contact with the engine block. This arrangement increases the possibility of undesirable relative movement between the liner and engine head which can result in head gasket failure or in the need for liner wall thickening which adds to the cost and decreases thermal conduction through the liner.
One approach for solving the above-noted problems is set forth in U.S. Pat. No. 4,244,330 issued to Baugh et al. and assigned to the assignee of the subject invention. Therein, the cylinder liner for an internal combustion engine includes a cylindrical hollow body having a press-fitted upper end and a stop located intermediate the liner ends for engaging an engine block liner stop to provide upper and lower seals for a coolant passage. The outside surfaces of the liner adjacent the press-fitted upper end and the stop are formed to permit a setable plastic material to be used between the liner and engine block to assist in forming the coolant seal and to provide radial support of the liner to permit the lower 30 percent of the cylinder liner to be free of any direct contact with the engine block. This design also permits use of a smaller capacity cooling system and improves lubricating oil flow within the engine block. In this regard, the only contact between the cylinder liner and engine block is that provided at the middle region of the cylinder liner and the interference fit about an upper periphery of the liner. In this regard, the thickness of the cylinder liner in the region adjacent the water jacket about an upper periphery of the cylinder liner must be of a size which can resist increased firing pressures and thermal loading of engines incorporating such liners. It is a primary object of the present invention to provide a cylinder liner wherein the thickness of the cylinder liner wall in this region can be reduced without sacrificing support of the liner to counteract high firing pressures on the order of 2,000 to 4,000 psi. Moreover, this wall thickness is reduced in a manner such that the bore diameter is increased without the need to increase the distance between cylinder centers thus increasing the sweep volume of existing engines.
U.S. Pat. No. 4,926,801 issued to Eisenberg et al. attempts to overcome a number of the above-noted shortcomings. Therein, a cylinder liner having a midstop arrangement is positioned within a bore and a cylinder block such that the lower two-thirds of the liner contact the cylinder block providing a dry type cylinder liner in this area. The upper portion or upper one-third of the liner is of a wet type and includes a plurality of flow passages for directing the flow of coolant about an outer periphery of the cylinder liner. The flow passages include thickened portions for increasing the strength of the upper portion of the cylinder liner, however, there is no support of the liner by the cylinder block in this area. Accordingly, depending upon the thickness of the cylinder liner in the upper region thereof, the liner may become distorted when subjected to heat generated by firing pressures in the range of 2,000 to 4,000 psi.
With reference to European Pat. Application No. 0 356 227 B1, a cooling system for a multi-cylinder engine is set forth wherein the cylinder liners include a plurality of axially aligned passages for aiding in the cooling of the an upper portion of the cylinder liner. The liner is of the top stop type and all of the aforementioned shortcomings associated with this type of liner continue to be of concern. Therein, the liner includes a plurality of cooling fins mounted at circumferentially spaced locations on the entire outer peripheral surface of the body of the wet liner such that when placed in close contact with the inner peripheral surface of the cylinder wall of the cylinder block, a plurality of rectilinear parallel cooling passages extending in the direction of the cylinder liner axis are obtained. The fins, however, are provided for directing coolant from a lower cooling gallery to a upper cooling gallery and do not provide support for the liner along its length in order to provide for an increase bore diameter without the need to increase the distance between cylinders liners.
Accordingly, there is clearly a need for a controlled cooled liner having a minimal wall thickness and a mid section support between a mid stop seat portion and a top deck portion in order to increase the cylinder bore diameter without increasing the distance between cylinder centers. Particularly, the controlled cooled liner would include a ring of lands positioned between vertical grooves formed in an outer wall portion of the liner which provide an interference fit between the liner and the engine block in the area between upper and lower cooling galleries. The grooves provide for the flow of coolant from a lower water gallery at an entry to the block to an upper water gallery at an exit from the block to prevent any overall cooling losses. In this regard, the thickness of the liner adjacent the coolant galleries can be reduced as compared to a conventional wet liner with the lands providing support to the mid section of the liner to prevent excessive liner deflection and cavitation when subjected to increase firing pressures in the range of 2,000 to 4,000 psi and the thermal loading associated with such pressures.